Donoway Sigma Xi Presentation 2015

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1. Effects of surface morphology on enhanced photoelectrochemical properties of nanocrystals Elizabeth Donoway 2. Solar Technology Current silicon-based solar panels Expensive Inefficient Prone to damage Silicon sheeted panels Unstable Large band gap Low energy output Small surface area Gupta, S. et al., 2013 3. Nanocrystals Larger surface area to volume ratio Regulated manipulation of characteristics Unique electrochemical properties Multi-faceted nanocrystals Configuration and structure determine stability {100}-bound cubes {111}-bound octahedrons Yang, Y. et al., Nanoscale, 2014, 6, 4316 4. New Solar Materials Cuprous oxide (Cu2O) Efficient Inexpensive Small band gap Unstable Polyvinylpyrrolidone (PVP) Capping molecule Stabilization of crystals Zhang, D. F. et al., Journal of Materials Chemistry, 2009, 19(29), 5220-5225. Van de Krol, R. et al., Journal of Materials Chemistry, 2008, 18(20), 2311-2320 5. Purpose Determine the effects of surface morphology on nanocrystal stability Fabricate Cu2O nanocrystals that are stable in solution Optimize nanocrystal morphology to create efficient materials for use in solar reactions 6. Methods Nanocrystal Synthesis Seeding of crystals from copper (II) chloride Addition of PVP to form octahedrons by truncating cube vertices Characterization TEM/SEM Imaging Electrode Preparation Adhesion of nanocrystals to FTO glass slides Photoelectrochemical Assays Controlled Potential Electrolysis (CPE) Determines electrode stability External Quantum Efficiency (EQE) Determines wavelengths of light that the solar panel is optimized for use in Solar Cell Efficiency 7. Results Characterization Cu2O Nanocubes Cu2O Nanooctahdrons Cu2O Nanocubes Cu2O Nanooctahedrons 8. Results Characterization Both nanocubes and nanocrystals were successfully fabricated TEM/SEM imaging confirmed that sizes and shapes of nanocrystals were differentiated, preventing agglomeration and sheeting, which would lower efficiency and reduce surface area available for light reactions to occur 9. Results Controlled Potential Electrolysis (Nanocubes) Single deposition of Cu2O nanocubes on FTO glass (average of 40 trials). CPE was conducted at increased energies equivalent to those exposed over a typical solar panel lifetime, corresponding to decades of solar cell use. Electrode samples were irradiated with solar light during two five- minute periods, alternating light and dark conditions in five second intervals. Dark DarkLight Light 10. Results Controlled Potential Electrolysis (Nanocubes) Single deposition of Cu2O nanocubes on FTO glass during light irradiation intervals. Light and dark conditions were alternated in five second intervals to ensure that electrodes remained stable during large fluctuations in photonic energy. Baseline photocurrent density (J) remained constant between solar irradiation periods during electrolysis. The obtention of photocurrent density away from the zero value during light irradiation over all 40 trials indicated maintained stability of electrodes. Light on Light off 11. Results Controlled Potential Electrolysis (Nanooctahedrons) Single deposition of Cu2O nanooctahedrons on FTO glass (average of 40 trials). Electrode samples were irradiated with solar light during two five-minute periods, alternating light and dark conditions in five second intervals. Exponential increase in magnitude of photocurrent density during light conditions indicates increased photocatalytic activity in nanooctahedron electrodes. Light LightDarkDark 12. Results Controlled Potential Electrolysis (Nanooctahedrons) Single deposition of Cu2O nanooctahedrons on FTO glass. Baseline remained constant between solar irradiation periods during electrolysis. Increase in photocurrent density magnitude away from the zero in all trials indicates maintained stability and increased photocatalytic response. Light off Light on 13. Results External Quantum Efficiency External quantum efficiency expressed as a percentage of photons absorbed and converted into electric current, modeled as a function of wavelength (nm). The longer range of wavelengths for which both Cu2O nanocrystal panels achieve 100% external quantum efficiency compared to Si- based cells indicates their optimization for use in the solar emission spectrum. [ ] Si-based 14. Results Solar Cell Efficiency Cu2O Electrode Efficiency max,theoretical =86% Cu2O Nanocube Efficiency Pmax=107.2 mW experimental=53.6% Cu2O Nanooctahedron Efficiency Pmax=125.4 mW experimental=62.7% Silicon Panel Efficiency max,theoretical=29% max,experimental=21.5% 15. Discussion Stability Stabilization of Cu2O via morphological manipulation of nanocrystals Both nanocubes and nanooctahedrons remained stable Photocurrent density magnitude increase in light condition 11 A cm-2 difference in magnitude between octahedron and cube electrodes Efficiency Nanocrystals optimized for use in solar emission spectrum Different morphologies demonstrate varied electrochemical properties Nearly 200% increase in efficiency over Si-based cells Applications Addresses instability of current materials New, inexpensive solar technologies made from Cu2O Cu2O cells are half as expensive to produce as Si-based cells 16. Future Research Assessment of photovoltaic cell performance and resistance to degradation under environmental conditions More specific evaluation of nanooctahedron morphology to further optimize nanocrystals for use in solar panels and increase panel efficiency Stabilization of alternate materials (e.g. graphene, germanium arsenide, titanium dioxide) for use in solar panels 17. Acknowledgements Joseph DuChene Dr. Wei David Wei Wei Research Group Student Science Training Program Pine Crest School Sigma Xi 18. References Borgohain, K., Murase, N., & Mahamuni, S. (2002). Synthesis and properties of Cu2O quantum particles. Journal of applied physics, 92(3), 1292-1297. De Jongh, P. E., Vanmaekelbergh, D., & Kelly, J. J. D. (2000). Photoelectrochemistry of Electrodeposited Cu2 O. Journal of The Electrochemical Society, 147(2), 486-489. Ho, J. Y., & Huang, M. H. (2009). 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